Contributions of Amine and Isocyanate-Rich Interlayers to Fiber–Matrix Adhesion for Carbon-Fiber-Reinforced Elastomeric Polyurethane Composites

Abstract

In the present research, the short carbon fiber (CF) surface was coated with polyamide (PA), polyetheramine-jeffamine (JA), polymeric MDI (MD), and cured-polymeric MDI (CM). For comparison, short carbon fibers were used before (unsized) and after applying sizing procedures such as Versamid, Jeffamine, isocyanate, and cured isocyanate. Surface characteristics of CF samples were evaluated using Fourier transform infrared (FTIR), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX) approaches. Tensile tests, hardness test, dynamic mechanical analysis (DMA), and melt-flow index (MFI) test were applied to CF-reinforced TPU composites, which were prepared with 5, 10, 15, and 20 wt% loading ratios using a lab-scale micro-compounder. Scanning electron microscopy (SEM) micro-images of selected composites were provided to investigate the dispersion quality of fibers in the polymer matrix. Sizing routes applied to the CF surface resulted in a considerable improvement in tensile strength and modulus of composites compared to unsized CF. On the contrary, substantial declines in the elongation of TPU were reported. The sized CF inclusions increased the shore hardness and storage modulus of unfilled TPU. The glass transition temperature (Tg) of TPU was elevated, as indicated by the Tan δ curves generated by the DMA study. SEM micro-images showed that sized CFs were dispersed homogeneously within the TPU phase, and their surfaces were fully coated with polymer; however, debonding was observed in unsized CF-containing composites. Among the sizing techniques used, isocyanate-sized CF samples yielded the best results and were identified as the most appropriate for the TPU/CF composite system.